OPTOELECTRONICS AND ADVANCED MATERIALS – RAPID COMMUNICATIONS Vol. 2, No. 12, December 2008, p. 855 - 858
Effect of thiourea on the optical properties of Di-sodium
hydrogen phosphate (DSHP) single crystal
M. N. RODE, S. S. HUSSAINIa, G. MULEY, B. H. PAWAR, M. D. SHIRSATa*
Department of Physics, University of Amravati, Amravati (MS) India
a
Optoelectronics and Sensor Research Laboratory, Department of Physics, Dr. Babasaheb Ambedkar Marathwada
University, Aurangabad -431 004(MS) India
Non linear optics (NLO) materials have acquired a new significance with the advent of a large number of devices utilizing
solid – state lasers sources and wide applications in the field of telecommunication, optical data storage and information
devices. The Di-sodium hydrogen phosphate (DSHP) is a well known inorganic NLO material for various optoelectronics
applications. In the present investigation we have grown thiourea doped Di- sodium hydrogen phosphate crystal from the
aqous solution. We could enhance the SHG efficiency of thiourea doped DSHP crystal. It was 2.2 times more than pure
DSHP. We observed the large enhancement in nonlinearity for high concentration of thiourea. The powder X-ray diffraction
analysis confirmed the crystal structure. The incorporation of thiourea in the grown crystal was qualitatively analyzed from
FT-IR study. The UV-Visible spectral study revealed that the incorporation of thiourea in DSHP enhances the transmittance
of DSHP. The thermal study of grown crystal was carried out by thermogravimetric analysis.
(Received November 20, 2008; accepted November 27, 2008)
Keywords: Crystal growth, DSHP, SHG efficiency, Optical properties
1. Introduction
Nonlinear optical materials are expected to be active
elements for optical communication and optoelectronics.
Intense attention has been paid to inorganic materials
showing the second order nonlinear optical effects because
of their higher nonlinearity. Among the nonlinear
phenomenon, frequency doubling, frequency mixing and
electro – optic modulation are important in the field of
optical image storage and optical communication [1-6].
The organic additive such as thiourea has emerged a new
class of promising nonlinear materials because of its
superior qualities over inorganic materials [7]. The Disodium hydrogen phosphate (DSHP) is an interesting
inorganic NLO material. M.Gunasekaran published his
work on growth and characterization of Di – Sodium
hydrogen phosphate [8].
The reason for choosing the thiourea as dopant is that
it has well known nonlinear property [9]. Thiourea belongs
to orthorhombic crystal system, its molecule is an
interesting inorganic matrix modifier due to its large
dipole moment and its ability to form an extensive
network of hydrogen bonds, and thiourea is typical polar
molecule [10].
In the present investigation, we have grown the
thiourea doped DSHP crystal with improved nonlinearity.
We observed high enhancement in SHG efficiency of
DSHP when it was mixed with 6 mole% thiourea.
Therefore 6 mole% thiourea doped DSHP crystal was
grown by slow evaporation solution growth technique.
Incorporation of thiourea in DSHP was analyzed by FT-IR
analysis. The optical study was carried out to observe the
optical absorption. The thermal behavior of grown crystal
was studied by thermogravimetric (TGA) analysis.
2. Experimental
2.1 Synthesis and growth
The Di -sodium hydrogen phosphate (DSHP) salt was
dissolved in Millipore water. The purity of salt was
obtained by repeated recrystallization. The solution of
DSHP salt was prepared in a slightly under saturation
condition. The solution was stirred well for six hours
constantly using magnetic stirrer, then solution was
filtered using Whatmann filter paper. The optically active
organic additative thiourea was added in 2,4and 6 mole
percent in different beakers of pure DSHP solution and
stirred well. The pure and thiourea doped DSHP solutions
were poured in different Petri dishes. We have harvested
seeds of these pure and thiourea doped DSHP crystal
within four to five days. The salts of 2, 4 and 6 mole
percent thiourea doped DSHP were subjected to SHG test
and we observed more enhancements for 6 mole percent of
thiourea.
Therefore the single crystal of 6 mole % thiourea
doped DSHP was grown by employing the slow
evaporation technique in constant temperature bath of
controlled accuracy ±0.01oC at temperature 35oC where
the super saturation was achieved. After the period of 25
days the large size crystal of thiourea doped DSHP crystal
was harvested. The photograph of grown crystal is shown
in Fig. 1.
856
M. N. Rode, S. S. Hussaini, G. Muley, B. H. Pawar, M. D. Shirsat
3.2 Powder X-ray diffraction
X-ray diffractometer analysis was carried out using
CuKα radiation λ = 1.5406ºA from a X-ray generator
setting 45kV, 40mA.The Powder samples was scanned in
steps of 0.02º for a time interval of 10.3377 sec over a 2θ
range of 10º to 120 º intensity. The X-ray pattern of the
thiourea doped DSHP samples is as shown in Fig. 2.
Fig. 1. 6 mole % thiourea doped DSHP crystal.
2.2 Characterization
The grown crystal was characterized by SHG
efficiency test, Powder X-ray diffraction, FTIR analysis,
UV-visible spectral studies and thermal analysis by
thermogravimetric analysis (TGA).
3. Results and discussion
3.1 SHG efficiency
In order to confirm the enhancement of nonlinearity of
DSHP due to addition of thiourea, the specimen was
subjected to Kurtz powder NLO test, which employed the
fundamental beam of wavelength “λ” 1064nm from Q
switched Nd: YAG laser. The out put from Nd: YAG laser
was used as a source and it was illuminated to the crystal
specimen. The laser input of 3mJ/pulse with repetition rate
of 10HZ and pulse width 8ns was used. The
photomultiplier tube was used as detector. The incident
beam was focused by a lens of focal length 6cm. The
scattered light was collected at 90ºto incident beam. The
second harmonic signals generated in the crystalline
sample were confirmed from emission of green radiation
by the sample. We have observed out put voltage of 4 mV
and 9 mV for pure DSHP and 6mole% thiourea doped
DSHP respectively. This indicates that the SHG efficiency
of 6 mole% thiourea doped DSHP is 2.25 times more than
pure DSHP. This indicates that the SHG efficiency of
thiourea doped DSHP crystal is high as compare to pure
DSHP. This is due to the fact that the sulfur present in
thiourea is more electro negative. This causes more
delocalization of electrons in case of thiourea doped DSHP
crystals. This increases the non centrosymmetric structure
of DSHP hence enhances its non linearity [11].
Fig. 2. Powder XRD pattern.
Table 1. Lattice parameter values of pure and thiourea
doped DSHP crystals.
Sample
a (A° )
b (A° )
c (A° )
V (A°3)
Pure DSHP
9.243
10.955
10.421
1051.8
Thiourea
8.204
11.018
10.442
939.44
doped DSHP
3.3 Fourier transformation infrared spectroscopy
(FTIR) analysis
The different functional groups present in the material
of grown crystal were detected from Fourier transform
infrared spectral study. The spectrum was recorded in the
wavelength range 600 -4000cm-1 using Perkin Elmer FTIR
spectrometer. The FTIR spectrum is shown in Fig. 3. The
band at 3747cm-1 may be due to the incorporation of added
NH2 group of thiourea [12]. The intense peak at 3442 cm-1
corresponds to P(O)-OH bond. The peak at 2985.65 cm-1 is
due to γ1 vibration belonging to a2 irreducible
representation [13]. The peak observed at 863.76 cm-1 may
be attributed to γ3 vibration of a1 representation. The γ7
vibration of e irreducible representation is observed 550.96
cm-1 .There is slightly changed in the vibrational frequency
of different functional groups of DSHP due to addition
thiourea [8].
Effect of thiourea on the optical properties of Di-sodium hydrogen phosphate (DSHP) single crystal
857
Fig. 4 (a, b). The spectra showing the 100%
transmittance in the thiourea doped DSHP crystal. It may
be due the more electro negativity of thiourea in
comparison of the sodium. Thus the thiourea doped DSHP
crystal can be used as better alternative to pure DSHP in
optoelectronics applications.
3.5 Thermogravimetric analysis (TGA)
Fig. 3. FTIR spectrum of thiourea doped DSHP crystal.
3.4 UV-Visible spectral study
The transmission spectrum plays a vital role in
identifying the potential of a NLO material because a
given NLO material can be utility only if it has a wide
transparency widow without any absorption at the
fundamental and second harmonic wave lengths preferably
with the lower limit of the transparency window being
well below the 300 nm limit [14]. The UV-visible spectral
studies of grown thiourea doped DSHP crystals were
carried out using Perkin Elmer spectrophotometer. The
transmission spectrum was recorded in the wavelength
region from 200 to 1200 nm and spectrums of thiourea
doped DSHP and pure and DSHP crystal are shown in
(a)
Thermo
gram
provides
information
about
decomposition pattern of materials and weight loss [15].
The thermo gravimetric methods are limited to
decomposition and oxidation reaction. Thermogravimetric
analysis of grown thiourea doped DSHP crystal was
carried out using TAQ-500 thermo gravimetric analyzer
between temperature limit -50°C to 800°C at a heating rate
of 25°C/min in a nitrogen inert atmosphere. The resulting
thermogram is shown in Fig. 5. There is weight loss of
about 50% between the temperature ranges 50°C to 100° it
may due to loss of water of crystallization and weakly
adsorbed one. There is minute loss occurred with the
maximum between the temperature limit from 100 to
300°C. The resulting residue is found to be thermally
stable without any decomposition.
Fig. 5. TGA thermogram of thiourea doped DSHP
crystal.
4. Conclusions
(b)
Fig. 4 (a). Transmittance spectrum of thiiourea doped
DSHP crystal ; (b). Transmittance spectra of pure DSHP
crystal.
The single crystal of thiourea doped DSHP crystal
was grown by slow evaporation solution growth method.
1. The powder XRD confirms its crystal structure.
2. The incorporation of thiourea in DSHP was
confirmed by FT-IR Study. The spectra revealed that due
to addition of thiourea the frequency vibration of different
functional group are slightly shifted.
3. The good optical transparency shows the possible
application of the material in the field of NLO.
4. The SHG test shows that the optically active carbon
in thiourea reacts with hydrogen of DSHP and enhanced
the non Centro symmetric structure of host and hence its
nonlinearity increases.
858
M. N. Rode, S. S. Hussaini, G. Muley, B. H. Pawar, M. D. Shirsat
5. The thermogravimetric analysis revealed that
thiourea doped DSHP crystal is thermally less stable than
pure DSHP.
Acknowledgements
The authors are thankful to the University Grants
Commission New Delhi, India for providing financial
assistance. Authors are grateful to Dr P.K. Das, Indian
Institute of Science, Bangalore (India) for SHG test.
References
[1] S. S. Hussaini, N. R. Dhumane, V. G. Dongre, P.
Ghughare, M. D. Shirsat, J. Optoelectron. Adv. Mater.
Rapid Comm. 1, 707 (2007).
[2] S. S. Hussaini, N. R. Dhumane, V. G. Dongre, M. D.
Shirsat, J. Optoelectron. Adv. Mater. Rapid Comm. 2,
108 (2008).
[3] N. R. Dhumane, S. S.Hussaini, V. V. Navarkhale, M.
D. Shirsat, Cryst. Res. Technol. 41, 897 (2006).
[4] M. D. Shirsat, S. S.Hussaini, N. R. Dhumane, V. G.
Dongre, Cryst. Res. Technol. 43, 756 (2008).
[5] N. R. Dhumane, S. S. Hussaini, V. G. Dongre,
Mahendra D. Shirsat, Optical material, Elsevier (In
Press).
[6] S. S. Hussaini, N. R. Dhumane, G. Rabbani, P.
Karmuse, V. G. Dongre, M. D. Shirsat, Cryst. Res.
Technol. 42, 1110 (2007).
[7] N. Vijayan, R. RameshBabu, M. Gunasekaran, R.
Gopalakrishana, P. Ramasamy, J. Cryst.Growth 256,
174 (2003).
[8] M. Gunasekaran, N. Vijayan, R. Ramesh Babu, R.
Gopalakrishanan, P. Ramasamy, C. W. Lan, J. Cryst.
Growth 244, 194 (2002).
[9] V. Crasta, V. Ravindrachary, R. F. Bhajantri, R.
Gonsalves, J. Cryst. Growth. 267, 129 (2004).
[10] N. P. Rajesh, V. Kannan, M. Ashok, K. Sivaji, P.
Santharaghavan, P. Ramasamy, J. Cryst. Growth 262,
561 (2004).
[11] C. K. Lakshamamna Perumal, A. Aruchakkarvarthi,
P. Santharaghvan, J. Cryst. Growth. 241, 200 (2002).
[12] R. Ramesh Babu, N. Vijayan, R. Gopalakrishnan, P.
Ramasamy, Cryst. Res. Technol. 41, 405 (2006).
[13] E. E. Berry, C. B. Baddiel, Spectrochim. Acta, Part A
23, 2089 (1967).
[14] S. Dhanuskodi, K. Vasantha, Cryst. Res. Technol.
39, 259 (2004).
[15] R. Ramesh Babu, N. Vijayan, R. Gopalakrishnan, P.
Ramasamy, J. Cryst. Growth. 240, 545. (2002).
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*
Corresponding author: [email protected]